Part hormone and part nutrient, vitamin D is essential for health. Here’s how to tell if you’re deficient, and what to do about it.
Vitamin D is critical for everything from bone health and immunity to hormone balance and mental wellness. Unfortunately, it’s also pretty common to be deficient in this key nutrient.
Most vitamin D comes from sitting out in the sun, without sunscreen. Even if everyone made sure to get outside enough, most of the planet doesn’t get enough year-round direct rays to raise blood levels.
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What is Vitamin D?
Vitamin D is technically a prohormone, which means it is a nutrient with hormone-like properties in the body. It can be manufactured by the body in response to direct sun exposure by interacting with cholesterol. (1) It is also known as a fat-soluble vitamin because it is stored in the body’s fat cells and it absorbs best when taken or eaten with fatty foods.
All cells have receptors to bind with vitamin D – it’s that crucial of a nutrient. Yet more than 1 billion people across the world have inadequate levels. (2) In the U.S. alone, more than 40 percent of all adults are deficient. (3)
There are several groups of people that are at higher risk of deficiency. They include:
- The elderly
- Those pregnant or breastfeeding
- Overweight or obese people
- People who spend little time outdoors, or wear sunscreen constantly
- Those who don’t eat enough dairy or fish
What Are Normal Levels?
The recommended daily intake of vitamin D is set between 400 to 800 IU, but most experts agree that this amount is too low to prevent true deficiency.
Depending on where you live, you may not be able to get vitamin D from the sun very often, as many locations get strong ultraviolet rays for less than half of the year. Plus, aging reduces the body’s ability to synthesize vitamin D, so even with adequate sun exposure, your levels could still be suppressed. (4)
How To Understand Your Lab Tests
In order to assess your vitamin D levels, doctors can run a lab test known as 25-vitamin D hydroxy or 25(OH)D. If you take vitamin D supplements, do not take them on the day of testing until after your blood has been drawn.
There is a very wide range that is considered “optimal” for vitamin D, and much will depend on who you ask and how healthy you are. Overall, research supports levels higher than 30 ng/mL for bone health, longevity, immune health, and more. According to Mayo Medical Laboratories, vitamin D levels are classed as such: (5)
- <10 – Severe deficiency
- 10-24 – Mild to moderate deficiency
- 25-80 – Optimal
- >80 – Possible toxicity
Signs and Symptoms of Vitamin D Deficiency
You might not know that you’re dealing with a vitamin D deficiency right away. Low levels might persist for months or years before there are signs. Once you reach that point, these are the most common giveaways that your vitamin D level might be too low.
There are many causes of fatigue, and vitamin D deficiency is one of them. (6) One case study identified severe vitamin D deficiency as the cause of “heavy daytime tiredness and pervasive fatigue”, which improved after the patient supplemented with dose-appropriate vitamin D. (7)
Other research confirms that vitamin D deficiency causes fatigue, with one study showing that women with levels lower than 30 ng/mL were more likely to be fatigued than those with levels higher than 30 ng/mL. (8)
2. Low Immunity
The immune system relies heavily on vitamin D to fight off bacterial infections and viral illnesses. When vitamin D levels are low, the immune system is ill-equipped to fully fight off invaders. (9)
Research finds a direct link between low levels of vitamin D and more frequent infections with colds, pneumonia, and bronchitis. (10, 11, 12) Fortunately, vitamin D supplements can help reduce that risk.
3. Bone and Muscle Pain
Pain in your bones or muscles can be indicative of low vitamin D levels. (13, 14) Research found that those deficient in vitamin D were almost twice as likely to experience pain in the legs, ribs, or joints compared to people whose vitamin D levels were considered normal. (15)
While it’s not always easy to pinpoint the cause of muscle pain, research finds that 71 percent of people experiencing chronic pain are low in vitamin D. (16, 17)
Vitamin D is closely associated with mental health, particularly warding off depression, and the risk gets higher as you age. (18) Because vitamin D has hormone-like properties, it can exert a powerful influence over neurotransmitters. Since depression also has ties to inflammation, it’s thought that vitamin D can cool the internal flame of an overactive immune system.
Research shows that supplementing with vitamin D during cold months and even in cases of seasonal affective disorder can improve symptoms of depression. (19)
5. Bone Loss and Osteoporosis
Aging impacts vitamin D stores and the body’s ability to synthesize vitamin D from sun exposure, but it also wreaks havoc on bone density and mineral stores. Still, excess calcium supplementation won’t fix all bone deficits. Vitamin D helps the body use calcium and when levels are low, it can demonstrate signs of deficiency.
Research shows a direct link between low bone density and low vitamin D levels. It’s not just calcium that your bones need, but adequate levels of vitamin D, too. (20)
How to Correct Vitamin D Deficiency
Very few foods have enough vitamin D in them to efficiently raise blood levels. Sun exposure is the best natural way to get vitamin D, but mushrooms, egg yolks, and fatty fish like salmon and mackerel are all good sources. (21)
If you’re very low in vitamin D, many doctors will recommend taking 50,000 IU of vitamin D once per week for a few weeks or a few months, depending on the severity of deficiency. For those without severely low levels, improvements can be made by supplementing with far lower doses, usually in the 2,000 to 4,000 range. (22)
Experts also recommend 10 to 20 minutes of sun exposure daily, without sunscreen, and with most of the trunk, arms, and legs bare. The more skin directly exposed to direct sunlight, the more likely your body will trigger the proper rise in blood levels. Individuals with darker skin tones may require more time in the sun for this synthesis to take place.
It’s important to talk to your doctor about your individual needs. If you’ve been cautioned against sun exposure for skin cancer or other reasons, ask about other ways you can maintain healthy vitamin D levels.
Vitamin D is a multifaceted nutrient that also acts as a hormone. Many adults are low in this critical nutrient, so it’s important to speak with your doctor if you’re experiencing any of the above symptoms. Direct sun exposure is the best way to get vitamin D but you can also supplement, as well as eat plenty of fatty fish, mushrooms, and egg yolks.